94 



is the tool with which, it works. 



In the "Ship-worms", i iio yo is a riarminx. gland in 

 the mantle of the posterior part of the body. A system of 

 hir;hly specialized muscles mar.ipulate che palettes and are 

 peculiar to Teredo. There is on either side but a half 

 ctenidium. The anterior ten filaments form small plica- 

 tions on the side of the "head", separated from the rest 

 of the gill by a long distance. In close association with 

 the gills is a prominent glandular structure of unknown 

 fi-inction. It consists of two typos of elements of remark- 

 able character. 



Through the elongation of the visceral mass, the posi- 

 tions of the two aortae have been reversed; i.e., the ap- 

 parent posterior aorta is the real anterior, and the ap- 

 parent anterior the real posterior. The caecum of tlie 

 stomach is very large and apparently an important absorb- 

 ent organ. The blind end of the style sheath is tubular ■ 

 and of very different character from the outer part. In 

 Xylotrya the typhlosole of the anterior part of the intos- 

 tine is remarkably developed. 



The nervous system contains the ihi'ee pairs of gan- 

 glia, v/ell developed, as in typical Lamollibranchs. The 



